Body vessel filter

ABSTRACT

A catheter-deliverable filter assembly deployable in a vessel of the body in alternatively a temporary configuration enabling the filter to be removed from the vessel or a permanent configuration, and a method for its use. The filter assembly comprises an elongated support carrying spaced along its length a filter element and a anchoring element with the filter element being spaced distally from the anchoring element. Each element comprises a core mounted to the elongated support and a plurality of flexible, resilient wires extending distally from the core, the wires having proximal portions attached at one end to the core and distal portions. The wires of the anchoring element include gripping elements for gripping the walls of a vessel. The wires are so configured as to support the apices of the filter and anchoring elements substantially in the center of the vessel. The filter assembly may include a hollow flexible tether releasably attached to the proximal end of the elongated support and having a distal end portion within which are resiliently confined the wires of the anchoring element when the filter element alone is deployed.

BACKGROUND OF THE INVENTION

Pulmonary embolism, in which emboli from any of various regions of thevascular system pass into the lungs, accounts for thousands of deathseach year in the United States. Blood clots from the lower extremitiesare commonly carried to the heart through the inferior vena cava, andthence to the lungs.

Many patients with documented pulmonary embolism can be treated withanti-coagulants to prevent further formation of thrombi, but there aresituations in which mechanical interruption of the inferior vena cava isthe preferred method to prevent pulmonary embolism. To prevent bloodclots from passing upwardly through the inferior vena cava, it has beensuggested to place filters in the vena cava which filter out bloodclots. An excellent but early description of vena cava filters is foundin Palestrant, Aubrey, M, et al. Comparative In Vitro Evaluation of theNitinol Inferior Vena Cava Filter, Radiology 145:351-355, November,1982. A more recent treatment of the subject of vena cava filters isfound in Interventional Radiology, 3^(rd) Edition, Castaeda-Zuniga,Wilfredo R., ed., Williams & Wilkins, Baltimore, pp 854-896 (1997).Various filters are disclosed in Lebigot, U.S. Pat. No. 4,781,177,Simon, et al., U.S. Pat. No. 5,669,933 and Maderlinger, U.S. Pat. No.5,720,764. Reference may be made also to Rasmussen, et al., U.S. Pat.No. 5,133,733, LeFebvre, U.S. Pat. No. 5,108,418, Goldberg, et al. U.S.Pat. No. 5,152,777 and El-Nounou, et al. U.S. Pat. No. 5,242,462.

In general, vena cava filters are introduced into the vasculaturethrough a puncture or an incision in a major vessel such as the internaljugular vein and the filter, elastically restrained in a deliverycatheter, is passed from the jugular vein through the right atrium ofthe heart and into the inferior vena cava whereupon the filter ismechanically expelled from the catheter and expands into contact withthe lumen. Various hook-like projections have been suggested for use inholding the filter in place once the delivery catheter has beenwithdrawn. When a filter using hooks, barbs and the like to retain it inplace permanently is thus to be removed, surgical intervention isusually required.

Temporary introduction of a vena cava filter may be desired to providerapid protection against pulmonary embolism, but as the conditionproducing blood clots is successfully treated, it may be desired toremove the filter from the vena cava. Vena cava filters commonly includea hub or central portion from which radiate outwardly a plurality ofwires, sometimes in a woven configuration, the wires serving to filterclots from blood flowing through the vein. It is not uncommon for thecentral portion of the filter element, which is to be near the center ofthe lumen, to have the greatest efficiency, that is, to have wires thatare closest together to thus produce smaller openings through whichblood flows. The screen openings often become larger toward the walls ofthe vein. For good results, it is desired that the center of the filterremain near the center of the vessel, but often this is not easilycontrolled and the center of the filter may tilt to one side or theother of the lumen, thus exposing the less efficient areas of the filterto blood flow at the center of the lumen and reducing filteringefficiency.

Also, it is sometimes difficult to visualize with accuracy theeffectiveness of a vena cava filter in filtering out blood clots.Commonly, an imaging or contrast medium such as Hipaque® (a product ofWinthrop Pharmaceutical) or Conray® (a product of Mallinckrodt) may beinjected upstream from the filter (that is, inferior to the filter inthe vena cava) in the course of obtaining a vena cavogram, but thecontrast liquid often becomes diluted in the blood stream as it reachesthe filter, preventing precise visualization of blood clots in thefilter. Moreover, to obtain a good vena cavogram, a large volume, e.g.,30 cc, of a contrast medium must be rapidly injected, and this procedureoften is done with the aid of a diagnostic catheter.

Although, as thus described, a variety of vena cava filters have beensuggested for use, the need remains for a filter that can be temporarilyinstalled in the vena cava for later removal, and for a filter enablingblood clots captured by it to be readily visualized by the introductionof a contrast medium. It would be particularly desirable to provide afilter assembly capable of deploying an easily removable filter element,but that may also deploy an anchoring element proximal to (that is,downstream from) the filter element, as warranted by a patient'scondition. It would also be desirable to provide a filter, the center orapex of which is positioned and maintained at or near the center of thelumen, so as to improve clot filtering efficiency. Moreover, it would bedesirable to provide a filter assembly enabling a contrast medium orother fluid to be injected upstream from the filter elements.

SUMMARY OF THE INVENTION

We have developed a filter assembly capable of deploying a filterelement or both a filter element and an anchoring element in vessels ofthe body such as the vena cava and other vessels of the body,particularly in the vasculature and especially in the larger vessels. Ina preferred embodiment, our filter assembly has a configuration thatenables apices of these elements to remain substantially in the centerof the lumen to improve filter efficiency, whether the filter assemblyis deployed in its temporary or permanent configuration. For ease ofexplanation, the filter assembly of our invention will be described inconnection with its use in the vena cava, but it will be understood thatthe filter assembly may be employed in various other vessels of thebody.

Our filter desirably is so constructed as to enable it to deploy adistal filter element in a temporary configuration or, in a permanentconfiguration, to add an anchoring element. When only the filter elementis deployed, the filter assembly remains attached to a tether thatenables the filter to be removed from the body or repositioned in thevessel. Upon deployment of the anchoring element, the tether is detachedand withdrawn, leaving the filter assembly comprising both the filterand anchoring elements in place in the vessel.

Thus, in one embodiment, the invention provides a catheter-deliverablefilter assembly for deployment in a vessel of the body in alternativelya temporary configuration in which only a filter element is deployedthat can be removed from or repositioned in the vessel or a permanentconfiguration in which an additional anchoring element is deployed whichgrips the walls of the vessel. The filter assembly comprises anelongated support having proximal and distal ends. Separate filter andanchoring elements are spaced axially along the support, and eachelement comprises a core carried by the support and a plurality offlexible, resilient wires having proximal portions attached to the coreand distal portions extending outwardly distally of the core andconfigured to resiliently contact walls of a vessel. The wires of eachelement converge proximally toward their respective cores to defineapices of the elements, the filter element being spaced distally of saidanchoring element. The anchoring element alone includes grippingelements adapted to grip the walls of a vessel to anchor the filterassembly in the vessel.

The filter assembly in one embodiment includes a hollow flexible tetherreleasably attached to the distal end of the elongated support andhaving a tubular, distal end portion within which are resilientlyconfined the wires forming said anchoring element when only the distalfilter element is deployed. The filter assembly desirably also includesa delivery catheter having an inner bore within which the core and wiresof the filter element are received in an elastically restrainedorientation to enable delivery of the filter assembly to the vessel,whereupon withdrawal of the delivery catheter enables the wires of thefilter element but not the anchoring element to be deployed in thevessel.

When the filter assembly has been properly placed within the vena cava,the delivery catheter is removed to deploy the wires of the filterelement, the wires of the anchoring element remaining confined withinthe hollow end portion of the tether. As so deployed in its temporary ortethered configuration, the filter can be withdrawn from the body easilyand without significant surgical intervention.

For deployment of the filter assembly in a permanent configuration, thehollow end portion of the tether is withdrawn proximally from theanchoring element to free its wires and enable them to expanddivergently from the anchoring element core to deploy within the vessel,the gripping elements carried by the anchoring element wires engagingthe surface of the lumen to anchor the filter assembly in the vena cavawith the apex of each element being supported by its wires substantiallyin the center of the vessel.

Accordingly, the invention in another embodiment comprises a method fordeploying a filter in the lumen of a patient's vessel. The methodcomprises the following steps:

a. A filter assembly is provided which includes an elongated supporthaving proximal and distal ends, and axially spaced filter and anchoringelements, each element comprising a core mounted coaxially to thesupport and having a plurality of flexible, resilient wires extendingdistally from its core. The anchoring element is spaced proximally fromthe filter element and has wires containing gripping elements forgripping the walls of a vessel. The assembly includes a deliverycatheter having an inner bore within which said filter element core andwires are slidably received in an elastically restrained orientation andhaving a distally open end. A flexible tubular tether is carriedslidably within the delivery catheter and has a hollow distal endportion releasably locked to the proximal end of the elongated support,the hollow distal end portion of the tether extending distally over andelastically restraining the wires of the anchoring element.

b. The delivery catheter is inserted into the vessel until its distalend is positioned adjacent the desired location for the filter element.The tubular tether, carrying at its distal end the elongated supporttogether with the filter and anchoring elements, is slidable within thedelivery catheter to deliver the elastically restrained filter elementwires to the distal end of the catheter.

c. The delivery catheter is proximally removed to free the wires of thefilter element to enable them to elastically contact the lumen of thevessel with the proximal portions of said wires converging proximally toform the apex of the filter element and with portions of the distal wireend portions of the filter element laying in line contact against andalong the lumen of the vessel for a distance sufficient to substantiallycenter said filter element apex in the lumen. If it is desired toreposition or remove the filter element, the wires of the filter elementmay be drawn back within the delivery catheter.

To deploy the anchoring element of the filter assembly, the methodincludes the step of unlocking and proximally withdrawing the hollowtether from the elongated support to thereby free the wires of theanchoring element from the hollow tether and enable them to elasticallydiverge into engagement with and grip the walls of the vessel to anchorthe filter assembly within the vessel, the wires of the anchoringelement converging proximally to form a second apex supportedsubstantially in the center of the vessel.

Preferably, the wires of each of the filter and anchoring elements areso disposed with respect to each other as to be out of contact with eachother distally of their respective apices when the filter assembly isdeployed in the lumen of a vessel. At least a portion of the length ofeach wire, desirably a distal end portion, may be spiraled axially inthe same direction (that is, either clockwise or counter-clockwise)about the axis of the elongated support to enable the wires to bereadily elastically collapsed for receipt within the delivery catheteror the hollow distal end of the tether, as the case may be, the spiralorientation of the wires enabling the wires to diverge upon release fromthe delivery catheter or tether into contact with the walls of the venacava without tangling of the wires with one another.

In a preferred embodiment, the elongated support is tubular and servesas an infusion tube that extends distally from the apex of the filterelement to enable a contrast medium or drug or other liquid to beinjected into the vena cava just distally of (that is, upstream from)the apex of the filter element so that the fluid immediately encountersany captured blood clots and enables them to be visualized or dissolvedor otherwise treated, as the case may require. In this embodiment, theflexible tether is tubular and is attached at its distal end to thetubular support in fluid communication therewith to supply contrastmedium or drug to the infusion tube, the proximal end of the tetherbeing accessible for this purpose outside the body. The elongatedsupport also may be made as a solid, preferably at least slightlyflexible rod, and the flexible tether in this embodiment may deliver acontrast medium or other liquid around, rather than through, theelongated support with the liquid in any event exiting into the vesselat or upstream from the apex of the filter element.

The line contact between the distal portions of the filter element wiresand the walls of the lumen serve not only to center the filter apex inthe lumen, but to also substantially center the distal end of theinfusion tube in the lumen, the infusion tube thus extendingsubstantially parallel to the vessel. Such line contact also inhibitspenetration of the walls of the vena cava by ends of the wire.

When only the filter element is deployed, the tether, which issufficiently stiff as to resist collapse in the vena cava, also servesto support, center, and maintain that filter element and infusion tubein its tethered configuration within the lumen of the vena cava. Thetether has a distal end portion that releasably and rigidly locks to thetubular support such that when the delivery catheter is removed, thetether will remain in place for the purpose of maintaining and centeringthe filter element within the vena cava and for supplying a liquid suchas a contrast medium just upstream from the filter element.

The unique characteristics of the filter deployment assembly of theinvention provide physicians, particularly interventional radiologists,with various options for deployment of the filter assembly in either itstemporary or permanent configuration. As described in greater detailbelow, the tether together with the filter assembly is slidably receivedwithin the delivery catheter with the filter element wires remainingelastically confined within the delivery catheter as the filter assemblyis moved within the delivery catheter. When the catheter has beenappropriately positioned within the vena cava, using routine centralvenous access techniques, the filter assembly is slidably moved to thedistal end of the delivery catheter, if it is not already there, and thedelivery catheter is removed proximally, freeing the filter elementwires which then elastically expand into contact with the walls of thevena cava. The resulting tethered or temporary configuration of thefilter assembly enables a fluid such as a contrast medium to be injectedfrom the hollow tether and through or around the elongated support, andalso permits the filter element to be repositioned in the vessel or tobe withdrawn proximally from the body, with the aid, if needed, of acatheter such as the delivery catheter that is passed over the tether toconfine the previously freed wire portions within the catheter.

If desired, the entire filter assembly may be deployed in the lumen bypassing it through a properly positioned delivery catheter, using adilator or other push-rod within the catheter.

To permanently deploy the filter assembly, a flexible release rod may beinserted into the tether and passed along into contact with the lockthat releasably locks the tether to the elongated support. Distalmovement of the rod with respect to the tether at this point unlocks thetether from the support. Withdrawal of the thus released tether whileholding the elongated support axially stationary with the release rodfrees the wires of the anchoring element from the confinement of thedistal end portion of the tether. Unconfined, the anchoring elementwires elastically expand radially, the wires in this configurationconverging at the filter core to form the apex of the permanentlydeployed filter. Gripping elements, such as proximally facing hooks,prongs or the like, are carried by the anchoring element wires. As thelatter wires are elastically pressed against the vessel walls, thegripping elements grip the walls to anchor the filter assembly in place.The filter assembly with both elements deployed is thus left behind as apermanently deployed filter assembly as the tether is removed from thebody. By “centrally disposed” or “approximately centered” or the like inconnection with the position of the apex of each element within thelumen, we mean that the apex is positioned within about the centralone-half, preferably the central one-third, of the diameter of thelumen.

The vena cava and other large vessels of the venous system are thinwalled and are easily perforated. The wires of the filter and anchoringelements, and preferably at least those of the filter element, mayterminate in enlarged ends which may be rounded or generally spheroidal,the enlarged ends inhibiting penetration of the walls of the vena cavaby the distal ends of the wires.

Upon deployment of only the filter element in the vena cava, with thetubular tether attached, the proximal end portion of the tether thatprotrudes from the entry site of the internal jugular vein or othervessel where catheter entry was gained can be buried beneath the skinfor a number of centimeters using known tunneling techniques, the woundover the entry site being closed to prevent infection. The proximal endof the tether protrudes from the skin at a location removed from theentry site and may terminate in an access element such as a controlledaccess hub of known design. The access element, such as a luer lock hub,provides immediate access to the tether for the purpose of delivering acontrast medium or other fluid just upstream from the filter element. Ifthe tether is to be removed, either in the course of withdrawing thefilter assembly from the vena cava or in the course of deploying thefilter assembly in its permanent configuration, as discussed above, theaccess element is detached, the entry site is surgically opened, theburied proximal length of the tether is easily withdrawn from thesubcutaneous tunnel, and the tether is then withdrawn from thevasculature.

In its tethered configuration, the filter element with its elongatedsupport serving as an infusion tube provides excellent access to theinterior of the vena cava at a location distal to or at the apex of thefilter element and preferably upstream therefrom. When a fluid isinjected for the purpose of visualizing a captured clot or formanagement of clots, it is anticipated that less fluid will be requiredbecause the fluid is concentrated at the clot location rather than beingdiffused in the blood flow far upstream from the filter. Moreover, useof the infusion tube for this purpose avoids the necessity of performinga costly and time consuming secondary site access procedure to utilize aseparate catheter. The infusion tube may be used for the infusion ofanticoagulants in clot management, for infusion of chemotherapy drugs,systemic antibiotics and for parenteral feeding, as well as enabling thecollection of blood samples.

It will be understood that it is important that the wires forming thefilter and anchoring elements, being bent as they are, be prevented fromrotating about their respective axes. The wires commonly are quite fine,in the order of 0.005 to about 0.025 inches (about 0.13 mm to about 0.6mm) in diameter, and it is difficult to mount the wires in bores formedin the cores in a manner preventing rotation of the wires in the bores.We have found that the wires can be easily attached to the cores in amanner that prevents their rotation, by providing a series ofcircumferentially spaced, axially extending bores through the cores,doubling a length of wire back upon itself to form two legs, andthreading the legs distally through different, preferably adjacent,circumferentially spaced bores in the core. Each of the wire lengths,then, forms two distally-extending wires.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a broken-away, side view of a filter assembly of the inventionwith only the filter element deployed;

FIG. 2 is a bottom end view of the filter assembly of FIG. 1, showingthe configuration of the wires;

FIG. 3 is a broken-away, side view of the filter assembly of FIG. 1 withboth the filter element and anchoring element wires deployed;

FIG. 3A is a broken-away view of a anchoring element wire with agripping element attached;

FIG. 4 is an exploded view of portions of the filter assembly of FIG. 1;

FIG. 5 is a broken-away view in partial cross-section showing elementsof the filter assembly of FIG. 1;

FIG. 6 is a broken-away cross-sectional view of a filter assembly of theinvention before deployment of the anchoring element thereof; and

FIG. 7 is a view similar to FIG. 6 but showing the anchoring element inan early stage of deployment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The wires employed in both the filter and anchoring elements areflexible and resilient, and are capable of being elastically deformedfrom a predetermined configuration (as where the wires, unconfined bythe tether or delivery catheter, are in contact with the walls of thevena cava) to another configuration (as when the wires are elasticallyconfined within the proximal end portions of the tether and catheter)and of elastically regaining, at least in part, their predeterminedconfiguration. The wires must be formed of a biocompatible material, ofcourse, and may for example be of stainless steel, cobalt-chromiumalloys, titanium, etc.

The filter wires may be formed of a superelastic alloy such as nitinol.Superelasticity refers to a phase transition that occurs in asuperelastic alloy such as nitinol when a deforming stress is externallyapplied. Nitinol, a near stoichiometric alloy of nickel and titanium, aswell as other superelastic alloys, (sometimes called shape memoryalloys), basically exists in either of two crystallographic forms. Whichform the alloy will be in depends upon several variables includingambient temperature, chemical composition and thermomechanical historyof the alloy. For nitinol, austenite is the parent phase, characterizedby a body centered cubic structure. Martensite is a transition phase andis characterized by a monoclinic crystalline structure. Generally,austenite will be present at a higher temperature than will martensite.As the temperature of a superelastic alloy in its austenite phase isreduced, a temperature M_(s) at which the austenite begins to transforminto martensite is reached, this temperature being referred to herein asthe transformation temperature.

Filter wires that are formed of a superelastic alloy preferably are inthe austenite phase at the temperature of use (body temperature) andundergo partial transformation to martensite when deformed by beingradially compressed for receipt within the tether or delivery catheter.Austenite will be transformed into martensite when the alloy is deformedby an external physical stress, this phenomenon sometimes being referredto as stress-induced martensite formation. The area of the alloy that isthus deformed will remain in the martensite phase as long as thedeforming force is maintained. When the stress is relieved, the deformedportion will tend to resume its original shape and in so doing willrevert back to the austenite phase. This phenomenon is the basis ofsuperelasticity.

Referring first to FIG. 3, a filter assembly of the invention isdesignated generally as 10 and includes an elongated, tubular support 20having open, distal and proximal ends 20.1, 20.2, respectively. Mountedin spaced relation along the elongated support 20 are filter andanchoring elements 6, 8, respectively, each including a generallycylindrical core 6.1, 8.1 from which extends a plurality ofcircumferentially spaced wires 6.2, 8.2, the wires of each elementextending distally and outwardly from their connections to theirrespective cores in desirably a generally conical configuration. Neartheir respective ends, the wires have sections 6.3, 8.3 bent in aslightly more distal direction to afford line contact with the vesselwalls. These sections, moreover, are oriented so as to spiral slightlyin the same rotational direction, as shown best in FIG. 2. The slightrotation accorded the ends 6.3 enables them to nest neatly when thewires are elastically compressed, as when they are captured in adelivery catheter.

The wires 8.2 of the proximal anchoring element 8 include along theirlengths gripping elements 8.4. The gripping elements can be of any typecapable of gripping to the walls of the vena cava or other vessel, andmay, for example, take the form of roughened portions of the wires 8.2.Preferably, the gripping elements 8.4 are formed as small barbs havinggenerally proximally oriented sharp ends 8.5. The barbs 8.4 may befashioned from the end portions of hypodermic needles having an interiordiameter closely receiving the wires, the barbs being crimped, welded,or otherwise fastened to the distal wire portions 8.3 to hold them inplace.

To prevent the ends of the wires from penetrating the walls of the venacava or other vessel, the wires desirably terminate distally inenlarged, bulbous or sphere-shaped ends 6.6, 8.6, which can be formed byknown melting procedures.

The assembly of the cores, wires and elongated support is shown best inthe exploded view of FIG. 4. In this figure, the core 6.1, which may beidentical to the core 8.1, is shown as being generally cylindrical inshape and having a central bore 6.7 sized to closely fit over theelongated support 20. The core may be affixed to the support 20mechanically as by crimping, chemically through the use of adhesives,thermally as by welding, etc. A series of circumferentially spaced bores6.8 are formed through the core parallel to its axis. We have found thatthe wires 6.2 can readily be affixed to the core securely and withoutpermitting the wires to rotate about their axes by forming a pair ofwires 6.2 from a single length of wire doubled back upon itself at itsmidpoint to form a U-shaped bend 6.9. The distal ends of the wires arereceived within the circumferentially spaced bores 6.8 of the core body,and preferably through adjacent bores 6.8, so that the wires protrudedistally from the distal end 7.0 of the core body with the U-shaped bend6.9 being adjacent the proximal end 7.1 of the core body. As required,the wires may be cemented, crimped, or otherwise fastened to the core torestrain any significant axial rotational movement of the wires in thebores 6.8. Axial movement of the wires relative to the cores may beprevented by subsequent heat treatment of the wires into their desiredgeometries.

Although the assembly of wires in the core, and mounting of the coreupon the elongated support 20, has been described in connection with thefilter element 6, it will be understood that the anchoring element 8 issimilarly assembled and mounted on the elongated support nearer itsproximal end 20.2, as shown best in FIG. 3. Desirably, the distal end20.1 of the elongated support is slightly flared at its end as an addedmeasure to deter the core 6.1 from escaping distally from the elongatedsupport 20. If desired, as when femoral access to the inferior vena cavais desired, the elongated support may be made from a solid rod ofplastic or other material, preferably flexible to aid in its placementin the lumen.

At its proximal end 20.2, the elongated support 20 is provided with atubular locking member 12, perhaps best shown in FIGS. 4 and 6. Thegenerally cylindrical locking member has an inner bore 12.3 enabling itto be snugly received on the elongated support 20, the lock 12 beingsecurely fastened to the elongated tubular support 20 adjacent itsproximal end 20.2. The latter end may be flared outwardly slightly tofurther deter escape of the tubular lock 12 proximally from theelongated support 20. The generally tubular lock 12 includes a pluralityof circumferentially spaced, distally extending fingers 12.2, which maybe simply formed by making U-shaped slits through the cylindrical wallsof the tubular lock as shown, and then bending the resulting fingersoutwardly slightly, as shown best in FIGS. 4 and 6. The lock 12 is madeof a springy material such that the fingers 12.2, when under no radiallydirected stress, occupy the position shown in FIG. 6, that is, thefingers extend radially outwardly slightly from the adjacent walls ofthe tubular lock and terminate distally in surfaces 12.3, the functionof which will be explained below. Particularly in the embodiment inwhich the elongated support is a solid rather than a tubular support,the connection between the tubular tether and the elongated support issufficiently loose, or is otherwise provided with openings, so thatimaging fluid or other liquid injected into the tether may exit from thedistal end of the tubular tether into the vessel approximately at orslightly upstream from the apex of the filter element.

Referring now to FIG. 1, which shows the filter assembly of theinvention with only the distal filter element 6 deployed, there isprovided a tether 26, the tether including a rigid distal constrainingtube portion 28 formed of metal or plastic or the like, and a long,flexible, tubular proximal portion 30. The latter may be a polymerictube having walls supported through the use of a coiled wire insert suchas that shown at 30.1 in FIG. 5, the latter being for the purpose ofmaintaining the tether portion 30 open and available for fluid flow asneeded. The tubular distal portion 28 of the tether terminatesproximally in an end portion 28.1 of reduced outer diameter, over whichthe distal end of the flexible tether portion is received, an adhesiveor swaging procedure or the like being used to fasten these portionssecurely together.

Just proximally of the proximal end 9.1 of the core 8.1, the innerdiameter of the rigid tether portion 28 is reduced to form a distallyfacing shoulder 28.2 which arrests relative proximal movement of thecore 8.1 within the tether. Proceeding proximally, the inner diameter ofthe tether portion 28 then increases abruptly to form a proximallyfacing shoulder 28.3. With reference to FIG. 6, it will be noted thatthe fingers 12.2 of the lock, when under no radially inwardly stress,occupy the position shown in FIG. 6; that is, the fingers extendradially outwardly slightly from the adjacent walls of the tubular lock.Distal ends 12.3 of the fingers thus come into contact with the annularshoulder 28.3 of the tether so as to prevent the tether from being drawnproximally with respect to the lock 32. Although various lockingmechanisms will be apparent to those skilled in the art, the lockingmechanism thus described has been found to be the most reliable inoperation.

Whereas FIG. 6 shows the release rod 36 positioned within the flexibletether 30 and approaching the tubular lock, in FIG. 7 the rim 36.2 ofthe release rod has cammed the resilient FIGS. 32.2 inwardly and out ofcontact with the annular shoulder 28.3. At this point, the tether may bewithdrawn proximally, that is, to the right in FIG. 7, from the lock 12and attached core and wires, the tether being withdrawn while therelease rod is held in an axially stationary position as shown so thecore 8.1 and the attached wires undergo little or no axial movement withrespect to the vessel walls. Proximal withdrawal of the tether portion28 permits the wires 8.2 of the anchoring element to deploy within thevessel, the barbs 8.5 or other gripping elements encountering andgripping to the walls of the vessel to restrain downstream movement ofthe filter assembly. Once the tether has been withdrawn sufficiently toenable the wires 8.2 to reach full deployment, both the tether and therelease rod may be removed. It will be understood that the amount ofcamming force needed to resiliently cam the fingers from the positionshown in FIG. 6 to the position shown in FIG. 7 is not great, and as aresult, the release rod 36 can easily be withdrawn proximally fromcontact with the fingers

The locking mechanism thus described may be unlocked, accordingly, byradially compressing the fingers 32.1 so they escape from the proximallyfacing shoulder 28.3 of the tether. This is accomplished through the useof a flexible, elongated release rod 36 which is slidably receivedwithin the tubular tether and which carries, at its forward or distalend, a distally open, rigid tubular portion 36.1 having an outerdiameter enabling it to be inserted within the proximal end 28.1 of thedistal end portion of the tether, and an inner diameter enabling it topass over the flared end 20.2 of the elongated support. The tubularportion 36.1 terminates distally in a rim 36.2 having an inner diameterwhich is not greater than the inner diameter of the annular shoulder28.3 and which encounters and cams radially inwardly the fingers 32.2 sothat their distal ends escape from the annular shoulder 28.3 of thetether. The distally open cavity 36.4 formed by the tubular end portion36.1 of the release rod includes a distally facing floor 36.3 soconfigured as to bear against the proximal end 20.2 of the elongatedsupport 20.

With reference again to FIG. 5, a delivery catheter 38 is employed todeliver the filter assembly within a vessel as desired. The deliverycatheter 38 has an inner diameter sufficient to slidably accommodate theflexible tether 30 and the elongated support 20 together with attachedcores and wires. With reference to FIGS. 1 and 5, it will be understoodthat the delivery catheter may be placed in the vessel so that itsdistal end 38.1 is positioned approximately at the desired site ofdeployment of the filter element 6. When the filter assembly is readyfor deployment within a vessel, the assembly, with attached flexibletether, is introduced into the delivery catheter, the wires of thefilter element 6 being compressed within the delivery catheter and theelastically compressed wires 8.2 of the anchoring element 8 beingconfined within the tubular end portion 28 of the tether. The filterassembly is advanced within the delivery catheter until the distal endsof the filter wires 6.2 are at the distal opening at the end 38.1 of thecatheter, whereupon withdrawal of the delivery catheter proximally ofthe filter assembly releases the wires of the filter element, enablingthem to expand resiliently into contact with walls of the lumen.Subsequent withdrawal of the tether, as explained above, releases thewires of the anchoring element so that they similarly expand intocontact with the walls of the lumen.

When both the filter and anchoring elements are deployed within avessel, the tubular support element 20 desirably is held substantiallyin the center of the vessel, with the apices of the elements similarlysupported substantially in the center of the vessel. By “apex”, as usedherein, we mean the point (actually, the small area) of convergence ofthe wires of each element. The apices of each element form the center ofthe element defined by the wires, and the wires of one element may bealigned axially with the wires of the other element, or not, as desired,and one or both cores 6.1, 8.1, may be mounted with rotational freedomon the elongated support. For a vessel of a given diameter, the size ofthe elements desirably are chosen such that their distal end portionslie along and preferably in line contact with the walls of the vessel inwhich the filter assembly is deployed to thereby position the apices ofthe respective elements near the center of the vessel and to enable thegripping elements of the anchoring element to properly deploy againstthe walls of the vessel.

The filter assembly of the invention can thus be readily deployed ineither of two configurations within the lumen of a vessel such as theinferior vena cava. The filter assembly itself can be deployed usingcommon catheter placement techniques of the type known in the medicalfield. Once the end of the filter element is in place, the deliverycatheter (shown at 38 in FIG. 5) is removed proximally to enable thefilter element 6 to be deployed. If the patient's medical conditionindicates that the filter assembly should remain permanently in the venacava, then the tubular tether is removed as described above. While inplace, however, the tether serves not only to maintain the filterelement in place, centered, but also as a convenient tube for supplyingan imaging fluid or other material to the infusion tube and forwithdrawing blood samples from the blood stream, as needed.

While a preferred embodiment of the present invention has beendescribed, it should be understood that various changes, adaptations andmodifications may be made therein without departing from the spirit ofthe invention and the scope of the appended claims.

What is claimed is:
 1. A filter assembly deployable in the lumen of avessel, the filter assembly comprising an elongated support havingdistal and proximal ends, a core attached to the elongated supportproximally of the distal end of the support and having a central axis,and a plurality of flexible, resilient wires extending distally from thecore to define a filter element and terminating distally of the distalend of the support, each wire having a proximal portion attached to thecore to define an apex and a distal portion extending distally from thecore, and a flexible hollow tether having a distal end portion locked tothe proximal end of the elongated support to enable a fluid to beejected distally of the filter apex.
 2. The filter assembly of claim 1wherein the distal end portion of the tubular tether includes an innerlip having a proximally facing surface and said elongated supportincludes a portion receivable proximally of said lip within the distalend portion of the tether and bearing a latch having a distally facingsurface engaging the proximally facing surface of the lip of the tetherto releasably lock the tether to the elongated support.
 3. The filterassembly of claim 2 wherein said latch is tubular and includes aplurality of radially resilient projections protruding radially from thelatch and positioned to be cammed radially inwardly by the rigid tubularportion of said lock release.
 4. The filter assembly of claim 3 whereinsaid radially resilient projections arise from the outer surface of thetubular latch and extend outwardly and distally, terminating distally insaid distally facing surface.
 5. The filter assembly of claim 2 whereinsaid lock release comprises a distally-open rigid tubular portion shapedto engage and cam said latch out of contact with said lip to unlock thetether from the elongated support.
 6. The filter assembly of claim 1wherein the distal end of said tether is releasably locked to theproximal end of the elongated tubular support and extends distally overand elastically confines said wires, the filter assembly including aflexible wire slidably received in said tether and carrying at itsdistal end a lock release for releasing the tether from the elongatedsupport to enable the tether to be withdrawn from elastic confinement ofthe wires and thereby enable the wires to elastically diverge distallyinto contact with walls of a vessel.
 7. The filter assembly of claim 1wherein said distal portions of the wires each have a length soconfigured as to spiral axially in the same direction when collapsed tofacilitate non-tangling release of the wires as they elastically divergedistally into contact with walls of a vessel.
 8. The filter assembly ofclaim 1 wherein the cross-sectional area of the distal portions of thewires is less that that of the proximal wire portions to provide thedistal wire portions with comparatively greater flexibility.
 9. Thefilter assembly of claim 1 wherein said core includes a plurality ofaxially extending bores spaced circumferentially of the central axis,and wherein an adjacent pair of said wires comprise the legs of a Ushaped wire length, the legs extending distally through adjacent ones ofsaid axially extending bores to lock each wire to the filter core and toprevent rotation of said wires about their respective axes within saidcircumferentially spaced bores.
 10. The filter assembly of claim 1,wherein the wires of the filter element terminate distally in enlargedends to restrain penetration of walls of a vessel.
 11. A filter assemblyfor deploying a filter in the lumen of a vessel, comprising a. anelongated support having proximal and distal ends, and axially spacedfilter and anchoring elements each comprising a core mounted coaxiallyto the support and a plurality of flexible, resilient wires extendingfrom the core and having proximal and distal portions, the distalportions being configured to lie against and along the walls of avessel, the anchoring element being spaced proximally from the filterelement and having wires containing gripping elements for gripping thewalls of a vessel; b. a flexible tubular tether having a hollow distalend portion releasably locked to the proximal end of the elongatedsupport and extending distally over and constraining the wires of saidanchoring element in an elastically collapsed orientation against theelongated support; c. a delivery catheter having an inner bore withinwhich said tether, elongated support and filter and anchoring elementsmay be slidably received, the wires of the filter element beingmaintained in an elastically collapsed orientation by the deliverycatheter until released into contact with walls of a vessel uponproximal withdrawal of the catheter from the filter element; d. aflexible wire slidably receivable in said tether and bearing at itsdistal end a lock release for releasing the tether from the elongatedsupport to enable the tether to be withdrawn from the anchoring elementand to thereby enable the wires of the anchoring element to engage andgrip the walls of the vessel.
 12. A catheter-deliverable filter assemblyfor deploying a filter element in a vessel of the body, comprising anelongated support having proximal and distal ends, separate filter andanchoring elements spaced axially along said support and each comprisinga core carried by the support and a plurality of flexible, resilientwires having proximal portions attached to the core and distal portionsextending distally of the core and configured to expand into resilientcontact with walls of a vessel, said wires converging proximally towardtheir respective cores to define apices of the respective elements, saidfilter element being spaced distally of said anchoring element, and saidanchoring element alone including gripping elements carried by distalportions of said wires and adapted to grip the walls of a vessel toanchor the filter assembly in the vessel, the filter assembly includinga hollow flexible tether releasably attached to the proximal end of thesupport and having a tubular, distal end portion within which areresilient confined the wires forming said anchoring element when onlythe distal filter element is deployed, said elongated support beingtubular and including open distal and proximal ends to define aninfusion tube extending distally from the filter element and having aproximal end in fluid communication with the hollow tether to enable afluid to be ejected distally of the filter element.
 13. Acatheter-deliverable filter assembly for deploying a filter element in avessel of the body, comprising an elongated support having proximal anddistal ends, separate filter and anchoring elements spaced axially alongsaid support and each comprising a core carried by the support and aplurality of flexible, resilient wires having proximal portions attachedto the core and distal portions extending distally of the core andconfigured to expand into resilient contact with walls of a vessel, saidwires converging proximally toward their respective cores to defineapices of the respective elements, said filter element being spaceddistally of said anchoring element, and said anchoring element aloneincluding gripping elements carried by distal portions of said wires andadapted to grip the walls of a vessel to anchor the filter assembly inthe vessel, the filter assembly including a hollow flexible tetherreleasably attached to the proximal end of the support, the distal endportion of the tether being releasably locked to said elongated support,the filter element including a flexible wire slidably received in saidtether and bearing at its distal end a lock release for releasing thetether from the support to enable the tether to be withdrawn from thefilter assembly.